US11644004B2 - Apparatus and method for extracting energy from a fluid - Google Patents

Apparatus and method for extracting energy from a fluid Download PDF

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Publication number
US11644004B2
US11644004B2 US16/342,888 US201716342888A US11644004B2 US 11644004 B2 US11644004 B2 US 11644004B2 US 201716342888 A US201716342888 A US 201716342888A US 11644004 B2 US11644004 B2 US 11644004B2
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flow
flow passage
control device
working fluid
water
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US20200056577A1 (en
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Thomas Denniss
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Wave Swell Energy Ltd
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Wave Swell Energy Ltd
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    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F03—MACHINES OR ENGINES FOR LIQUIDS; WIND, SPRING, OR WEIGHT MOTORS; PRODUCING MECHANICAL POWER OR A REACTIVE PROPULSIVE THRUST, NOT OTHERWISE PROVIDED FOR
    • F03B—MACHINES OR ENGINES FOR LIQUIDS
    • F03B13/00—Adaptations of machines or engines for special use; Combinations of machines or engines with driving or driven apparatus; Power stations or aggregates
    • F03B13/12—Adaptations of machines or engines for special use; Combinations of machines or engines with driving or driven apparatus; Power stations or aggregates characterised by using wave or tide energy
    • F03B13/14—Adaptations of machines or engines for special use; Combinations of machines or engines with driving or driven apparatus; Power stations or aggregates characterised by using wave or tide energy using wave energy
    • F03B13/141—Adaptations of machines or engines for special use; Combinations of machines or engines with driving or driven apparatus; Power stations or aggregates characterised by using wave or tide energy using wave energy with a static energy collector
    • F03B13/142—Adaptations of machines or engines for special use; Combinations of machines or engines with driving or driven apparatus; Power stations or aggregates characterised by using wave or tide energy using wave energy with a static energy collector which creates an oscillating water column
    • E—FIXED CONSTRUCTIONS
    • E02—HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
    • E02B—HYDRAULIC ENGINEERING
    • E02B9/00—Water-power plants; Layout, construction or equipment, methods of, or apparatus for, making same
    • E02B9/08—Tide or wave power plants
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01D—NON-POSITIVE DISPLACEMENT MACHINES OR ENGINES, e.g. STEAM TURBINES
    • F01D15/00—Adaptations of machines or engines for special use; Combinations of engines with devices driven thereby
    • F01D15/10—Adaptations for driving, or combinations with, electric generators
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F03—MACHINES OR ENGINES FOR LIQUIDS; WIND, SPRING, OR WEIGHT MOTORS; PRODUCING MECHANICAL POWER OR A REACTIVE PROPULSIVE THRUST, NOT OTHERWISE PROVIDED FOR
    • F03B—MACHINES OR ENGINES FOR LIQUIDS
    • F03B11/00—Parts or details not provided for in, or of interest apart from, the preceding groups, e.g. wear-protection couplings, between turbine and generator
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F03—MACHINES OR ENGINES FOR LIQUIDS; WIND, SPRING, OR WEIGHT MOTORS; PRODUCING MECHANICAL POWER OR A REACTIVE PROPULSIVE THRUST, NOT OTHERWISE PROVIDED FOR
    • F03B—MACHINES OR ENGINES FOR LIQUIDS
    • F03B11/00—Parts or details not provided for in, or of interest apart from, the preceding groups, e.g. wear-protection couplings, between turbine and generator
    • F03B11/02—Casings
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F03—MACHINES OR ENGINES FOR LIQUIDS; WIND, SPRING, OR WEIGHT MOTORS; PRODUCING MECHANICAL POWER OR A REACTIVE PROPULSIVE THRUST, NOT OTHERWISE PROVIDED FOR
    • F03B—MACHINES OR ENGINES FOR LIQUIDS
    • F03B13/00—Adaptations of machines or engines for special use; Combinations of machines or engines with driving or driven apparatus; Power stations or aggregates
    • F03B13/12—Adaptations of machines or engines for special use; Combinations of machines or engines with driving or driven apparatus; Power stations or aggregates characterised by using wave or tide energy
    • F03B13/14—Adaptations of machines or engines for special use; Combinations of machines or engines with driving or driven apparatus; Power stations or aggregates characterised by using wave or tide energy using wave energy
    • F03B13/24—Adaptations of machines or engines for special use; Combinations of machines or engines with driving or driven apparatus; Power stations or aggregates characterised by using wave or tide energy using wave energy to produce a flow of air, e.g. to drive an air turbine
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F03—MACHINES OR ENGINES FOR LIQUIDS; WIND, SPRING, OR WEIGHT MOTORS; PRODUCING MECHANICAL POWER OR A REACTIVE PROPULSIVE THRUST, NOT OTHERWISE PROVIDED FOR
    • F03B—MACHINES OR ENGINES FOR LIQUIDS
    • F03B13/00—Adaptations of machines or engines for special use; Combinations of machines or engines with driving or driven apparatus; Power stations or aggregates
    • F03B13/12—Adaptations of machines or engines for special use; Combinations of machines or engines with driving or driven apparatus; Power stations or aggregates characterised by using wave or tide energy
    • F03B13/26—Adaptations of machines or engines for special use; Combinations of machines or engines with driving or driven apparatus; Power stations or aggregates characterised by using wave or tide energy using tide energy
    • F03B13/266—Adaptations of machines or engines for special use; Combinations of machines or engines with driving or driven apparatus; Power stations or aggregates characterised by using wave or tide energy using tide energy to compress air
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F05—INDEXING SCHEMES RELATING TO ENGINES OR PUMPS IN VARIOUS SUBCLASSES OF CLASSES F01-F04
    • F05B—INDEXING SCHEME RELATING TO WIND, SPRING, WEIGHT, INERTIA OR LIKE MOTORS, TO MACHINES OR ENGINES FOR LIQUIDS COVERED BY SUBCLASSES F03B, F03D AND F03G
    • F05B2210/00—Working fluid
    • F05B2210/10—Kind or type
    • F05B2210/12—Kind or type gaseous, i.e. compressible
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F05—INDEXING SCHEMES RELATING TO ENGINES OR PUMPS IN VARIOUS SUBCLASSES OF CLASSES F01-F04
    • F05B—INDEXING SCHEME RELATING TO WIND, SPRING, WEIGHT, INERTIA OR LIKE MOTORS, TO MACHINES OR ENGINES FOR LIQUIDS COVERED BY SUBCLASSES F03B, F03D AND F03G
    • F05B2210/00—Working fluid
    • F05B2210/40—Flow geometry or direction
    • F05B2210/404—Flow geometry or direction bidirectional, i.e. in opposite, alternating directions
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F05—INDEXING SCHEMES RELATING TO ENGINES OR PUMPS IN VARIOUS SUBCLASSES OF CLASSES F01-F04
    • F05B—INDEXING SCHEME RELATING TO WIND, SPRING, WEIGHT, INERTIA OR LIKE MOTORS, TO MACHINES OR ENGINES FOR LIQUIDS COVERED BY SUBCLASSES F03B, F03D AND F03G
    • F05B2220/00—Application
    • F05B2220/70—Application in combination with
    • F05B2220/706—Application in combination with an electrical generator
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F05—INDEXING SCHEMES RELATING TO ENGINES OR PUMPS IN VARIOUS SUBCLASSES OF CLASSES F01-F04
    • F05B—INDEXING SCHEME RELATING TO WIND, SPRING, WEIGHT, INERTIA OR LIKE MOTORS, TO MACHINES OR ENGINES FOR LIQUIDS COVERED BY SUBCLASSES F03B, F03D AND F03G
    • F05B2250/00—Geometry
    • F05B2250/02—Geometry variable
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F05—INDEXING SCHEMES RELATING TO ENGINES OR PUMPS IN VARIOUS SUBCLASSES OF CLASSES F01-F04
    • F05B—INDEXING SCHEME RELATING TO WIND, SPRING, WEIGHT, INERTIA OR LIKE MOTORS, TO MACHINES OR ENGINES FOR LIQUIDS COVERED BY SUBCLASSES F03B, F03D AND F03G
    • F05B2270/00—Control
    • F05B2270/10—Purpose of the control system
    • F05B2270/20—Purpose of the control system to optimise the performance of a machine
    • F05B2270/202—Tuning to wave conditions
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E10/00—Energy generation through renewable energy sources
    • Y02E10/30—Energy from the sea, e.g. using wave energy or salinity gradient
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P80/00—Climate change mitigation technologies for sector-wide applications
    • Y02P80/10—Efficient use of energy, e.g. using compressed air or pressurized fluid as energy carrier

Definitions

  • This disclosure relates generally to energy generation and more particularly, but not exclusively, to energy generation using ocean wave energy extraction systems.
  • the disclosure is concerned with the design of the apparatus as well as methods for optimising the capture of energy from such apparatus.
  • wave power generation systems Numerous types of wave power generation systems have been proposed in the art. Such systems are based on the principle of using the motion of waves to cause a rotary movement of a turbine to drive a generator to produce electricity.
  • Known wave power generation systems employ one or more fluid flow ducts for containing oscillating water columns (OWC) connected to a turbine. In such systems there is frequently reversing air flow conditions present caused by displacement of the air in a duct, as a result of the oscillatory motion of the waves in the OWC caused by inward and outward flows of waves.
  • OWC oscillating water columns
  • These turbines often have the disadvantage that they are complex in configuration and expensive to manufacture, and cannot withstand the harsh environmental conditions (salt water, high or rough seas bringing large or unpredictable forces) over long periods of time. Many of these prior systems operate at low efficiency due to losses when converting the motion of the OWC into rotational mechanical energy in the bidirectional turbines.
  • an apparatus for extracting energy from an oscillating working fluid comprising a flow passage for the working fluid, a turbine and a flow control device, each of the turbine and the flow control device being in direct fluid communication with the flow passage, wherein in use the flow control device is selectively moveable between a first configuration in which the flow control device is open to allow a flow of the working fluid to exit the flow passage therethrough, and a second configuration in which the flow control device restricts a flow of the working fluid therethrough, such that the working fluid enters the flow passage via the turbine.
  • the flow control device changes the configuration of access to the flow passage in response to changes in the pressure and/or direction of flow of the oscillating working fluid.
  • the flow control device is fully closable so as to facilitate the flow of working fluid solely via the turbine in the second configuration.
  • the flow control device is fitted with a control mechanism to control its movement between the first and second configurations.
  • the flow control device has an element which is moveable by the control mechanism to become open and closed to the flow of working fluid.
  • the element is one of hingedly, slidably or rotatably moveable, and is of a shape which covers a cross-sectional opening passage of the flow control device.
  • the flow control device is one of a butterfly valve or a check valve.
  • the turbine includes a rotor comprising a central hub and a plurality of blades arranged about and extending from the periphery of the hub, the rotor disposed within a housing connected to the flow passage, whereby the shape of the blades and their orientation in relation to the hub facilitates unidirectional rotation of the turbine rotor in response to a unidirectional axial flow of working fluid through the housing.
  • an electric generator is configured for rotation by the turbine to generate electrical energy.
  • a drive shaft is coupled to the hub at its proximal end and to the electric generator at its distal end.
  • the working fluid is air
  • the flow of the air is generated by oscillations of an oscillating water column which is in fluid communication with the flow passage, and which is located in a duct.
  • the duct comprises: (a) a first portion arranged in use to be substantially submerged below the mean surface level (MSL) of a body of water in which it is located, the first portion having an opening arranged for receiving an incoming wave from the body of water, and (b) a second portion which depends from the first portion and which is arranged in use to extend above the MSL, the second portion for receiving water from the incoming wave after it flows through the first portion, wherein the flow passage is defined by a region of the second portion which extends above a maximum level of water received from the incoming wave after it flows through the first portion.
  • MSL mean surface level
  • the first and second portions of the duct are joined via a flow direction control segment intermediate the first and second portions, the flow direction control segment is defined by a planar sloped portion arranged at the junction of and extending between the first and second portions.
  • the first and second portions of the duct are generally elongate conduits, the first portion having a cross-sectional area greater than the cross-sectional area of the second portion.
  • the cross-sectional area at the opening of first portion is of a greater cross-sectional area than the remainder of the first portion, the conduit tapering down in cross-sectional area when moving in a direction from an outer entry mouth region at the opening toward the second portion, so as to accelerate the flow of incoming waves from the body of water into the duct.
  • the outer entry mouth region of the first portion is arranged in use to extend above the MSL of a body of water in which it is located, so as to capture a greater flow of incoming waves from the body of water into the duct.
  • the duct is operable to rest on the floor of the body of water in which it is disposed.
  • a wave energy extraction system including:
  • duct for receiving an oscillating water column
  • the duct comprising: (i) a first portion arranged in use to be substantially submerged below the mean surface level (MSL) of a body of water in which it is located, the first portion having an opening arranged for receiving an incoming wave from the body of water, and (ii) a second portion which depends from the first portion and which is arranged in use to extend above the MSL, the second portion for receiving water from the incoming wave after it flows through the first portion, such that in use an oscillating water column is established within the duct as a result of repeated movement of water into and out of the duct, the flow of water out of the duct also being via the opening, but in a direction opposite to the direction of the incoming wave;
  • MSL mean surface level
  • At least one flow control device which is also in direct fluid communication with the said flow passage, the flow control device being arranged in use to move between a first configuration in which the device is open, allowing a flow of displaced air to exit the flow passage when the oscillating water column is received into the second portion of the duct, and then to a second configuration in which the device restricts air flowing into the second portion, whereupon, as the oscillating water column flows out of the duct in the said opposite direction, a flow of air is drawn back into the flow passage via the rotatable air turbine.
  • the flow control device changes the configuration of access to the second portion in response to changes in the pressure and/or direction of flow of the oscillating working fluid.
  • the system further includes an electric generator configured for rotation by the turbine to generate electrical energy.
  • the turbine includes a rotor comprising a central hub and a plurality of blades arranged about and extending from the periphery of the hub, the rotor disposed within a flow passage connected to the second portion, whereby the shape of the blades and their orientation in relation to the hub facilitates unidirectional rotation of the turbine rotor in response to axial air flow through the flow passage into the second portion.
  • a drive shaft is coupled to the hub at its proximal end and to the electric generator at its distal end.
  • the frequency of the oscillating water column in use can be varied by changing the cross-sectional area of the flow control device(s) as a proportion of the surface area of the second portion which extends above the MSL, by the selective movement of one or more of the flow control device(s) between the first and second configurations.
  • the cross-sectional area of the flow control device(s) as a proportion of the surface area of the second portion which extends above the MSL is arranged to be less than 15 percent. In a particular form of this, the said proportion is arranged to be less than 10 percent.
  • system of the second aspect includes the apparatus as defined in the first aspect.
  • embodiments are disclosed of a method of controlling the frequency of movement of water in an oscillating water column to substantially correspond to the frequency of an incoming and outgoing wave from a body of water which is in fluid communication with the column, the method comprising the steps of:
  • a duct for receiving the oscillating water column comprising: (i) a first portion arranged in use to be substantially submerged below the mean surface level (MSL) of the body of water in which it is located, the first portion having an opening arranged for receiving the incoming wave from the body of water, and (ii) a second portion which depends from the first portion and which is arranged in use to extend above the MSL, the second portion for receiving water from the incoming wave after it flows through the first portion, such that the oscillating water column is established in use within the duct as a result of repeated movement of water into and out of the duct, the flow of water out of the duct also being via the opening, but in a direction opposite to the direction of the incoming wave; and
  • MSL mean surface level
  • the method further comprises the step of continuously adjusting the configuration of the at least one flow control device(s) in response to changes in the frequency of the incoming and outgoing wave, by means of a control mechanism.
  • the control mechanism selectively moves one or more of the flow control device(s) between the first and second configurations.
  • the duct, the flow control device and the control mechanism of the third aspect are as defined in the first aspect.
  • a duct for receiving an oscillating water column comprising: (a) a first portion arranged in use to be substantially submerged below the mean surface level (MSL) of the body of water in which it is located, the first portion comprising a conduit having an opening arranged for receiving the incoming wave from the body of water, and (b) a second portion comprising a further conduit which depends from the first portion and which is arranged in use to extend above the MSL, the second portion for receiving water from the incoming wave after it flows through the first portion, wherein an entry mouth at the opening of the first portion is arranged in use to partially extend above the MSL of a body of water in which it is located, so as to capture a greater flow of incoming waves from the body of water into the duct.
  • MSL mean surface level
  • the first portion has a greater cross-sectional area at the opening than the remainder of the first portion, the conduit tapering down in cross-sectional area when moving in a direction from the entry mouth at the opening toward the second portion, so as to accelerate the flow of incoming waves from the body of water into the duct.
  • the uppermost and outermost in use region of the entry mouth of the first portion is arranged in use to partially extend above the MSL of the body of water.
  • an uppermost surface of the first portion slopes downwardly when moving in a direction from the entry mouth at the opening toward the second portion.
  • the duct of the fourth aspect is otherwise as defined in the first aspect.
  • inventions are disclosed of apparatus for extracting energy from an oscillating working fluid, the apparatus including: a housing defining a flow passage for the working fluid; an energy conversion unit disposed at the housing, in fluid communication with the working fluid in the flow passage in use; and a flow control means which is in fluid communication with the flow passage, in use for selectively changing the configuration of the flow passage between an active configuration in which the working fluid acts on the energy conversion unit, and a bypass configuration in which the working fluid bypasses the energy conversion unit.
  • the flow control means and the energy conversion unit are configured to operate sequentially such that a flow of working fluid exits the flow passage via the flow control means, and a flow of working fluid enters the flow passage via the energy conversion unit.
  • the housing is arranged to contain an oscillating water column located adjacent the sea, and the direction of the working fluid acting on the energy conversion unit is associated with the fall of a passing wave.
  • the energy conversion unit includes a turbine rotor.
  • the apparatus of the fifth aspect is otherwise as defined in the first aspect.
  • embodiments are disclosed of a method of extracting energy from an oscillating working fluid, the method including the steps of:
  • the method of the sixth aspect is otherwise as defined in the third aspect.
  • embodiments are disclosed of a method for locating an oscillating wave column energy capture device at an offshore location in a body of water, the method including the steps of:
  • the energy capture device is otherwise as defined in the first or fifth aspects.
  • MSL is used for “mean surface level” or “mean sea level”, and is defined as the mid-point between a mean low and a mean high tide in a body of water at a particular location. MSL therefore means an average level of the surface of a particular body of water, and thus also represents a vertical depth datum point from which variations in wave crests or troughs can be measured.
  • FIG. 1 is a front, perspective, schematic view of an apparatus for extracting energy from an oscillating fluid, such as a wave from a body of water, in accordance with a first embodiment of the present disclosure
  • FIG. 2 is a rear, perspective schematic view of the apparatus according to FIG. 1 ;
  • FIG. 3 A is a schematic, partial cross-sectional, side elevational view of the apparatus according to FIG. 1 , when viewed along a sectional plane A-A which is orthogonal to the MSL, and at the moment of inception of a wave moving toward the apparatus;
  • FIG. 3 B is a schematic, partial cross-sectional, side elevational view of the apparatus according to FIG. 1 , when viewed along a sectional plane A-A which is orthogonal to the MSL, and at the moment a wave moves through the apparatus, and gas is displaced and flows out of the fluid control device(s);
  • FIG. 3 C is a schematic, partial cross-sectional, side elevational view of the apparatus according to FIG. 1 , when viewed along a sectional plane A-A which is orthogonal to the MSL, and at the moment a wave moves back out the apparatus toward the body of water, the fluid control device(s) are closed, and gas is drawn in a flow through a unidirectional turbine, to turn the turbine and to generate electrical energy;
  • FIG. 4 is a front, perspective, schematic view of an apparatus for extracting energy from an oscillating fluid, such as a wave from a body of water, in accordance with a further embodiment of the present disclosure
  • FIG. 5 is a rear, perspective schematic view of the apparatus according to FIG. 4 , depicting the lowermost inlet region to the interior of the oscillating wave column, and the wave-piercing lip;
  • FIG. 6 is a schematic, partial cross-sectional, side elevational view of an apparatus for extracting energy from an oscillating fluid, such as a wave from a body of water, in accordance with a further embodiment of the present disclosure; the drawing depicts the moment a wave moves through the apparatus, and gas is displaced and flows out of the fluid control device(s) (inset photo, valves open);
  • FIG. 7 is a schematic, partial cross-sectional, side elevational view of the apparatus according to FIG. 6 ; the drawing depicts the moment a wave moves back out the apparatus toward the body of water, the fluid control device(s) are closed, and gas is drawn in a flow through a unidirectional turbine, to turn the turbine and to generate electrical energy;
  • FIG. 8 is a front, perspective, schematic view of an apparatus for extracting energy from an oscillating fluid, such as a wave from a body of water, in accordance with a further embodiment of the present disclosure; said wave energy collection apparatus being shown positioned on a floating dock which is submersible. In a non-submerged state the dock is able to be moved by towing behind a shipping vessel for in-water location of the apparatus.
  • the oscillating wave column device is itself fitted with flotation aids;
  • FIG. 9 is a front, perspective, schematic view of the apparatus for extracting energy in accordance with FIG. 8 , said apparatus being positioned on the said submersible floating dock which is depicted in the non-submerged position, and now the apparatus and the dock are shown being towed behind a shipping vessel in the form of a tugboat, in a direction toward the pre-determined destination of the apparatus on the body of water;
  • FIG. 10 is a front, perspective, schematic view of the apparatus for extracting energy in accordance with FIG. 8 , said apparatus now shown separated from the submersible floating dock.
  • the dock is depicted as having been lowered in the water so that the apparatus (floated by means of its flotation aids in the form of buoy panels) can then be dragged forward and separated from the dock;
  • FIG. 11 is a front, perspective, schematic view of the apparatus for extracting energy in accordance with FIG. 8 , said apparatus now shown separated from the submersible floating dock, and the dock has now been raised up in the water again, and is floating.
  • the tugboat tows the wave energy collection unit forward, and away from the dock.
  • FIG. 12 is a front, perspective, schematic view of the apparatus for extracting energy in accordance with FIG. 8 , said apparatus now shown as being partially submerged by means of removal of some of the buoy panel elements (flotation aids) from its outer side walls. This is because the apparatus has now been moved to its pre-determined end use location in the body of water. The unit settles into its position on the shoreline sea floor.
  • FIG. 13 is a front, perspective, schematic view of the apparatus for extracting energy in accordance with FIG. 8 , said apparatus now shown as partially submerged in its final position in the water, resting on the sea floor, where it will capture waves and generate energy. All buoy panel elements (flotation aids) have been removed from its sides. The floating dock, and the buoy panels are all shown being removed by the tugboat, for repeated use.
  • FIG. 14 is a front, top, perspective, schematic view of an apparatus for extracting energy from an oscillating fluid, such as a wave from a body of water, in accordance with a further embodiment of the present disclosure; the apparatus is shown positioned in a body of surrounding water;
  • an oscillating fluid such as a wave from a body of water
  • FIG. 15 is a front, perspective, schematic view of an apparatus of FIG. 14 ; the apparatus is shown positioned in a body of surrounding water; this shows more detail of the turbine atop the apparatus;
  • FIG. 16 is a graph showing a predicted efficiency curve for the large scale prototype unidirectional air turbine being developed, based on the apparatus of the present disclosure
  • FIG. 17 is a graphical depiction of the energy balance found for a vented oscillating water column device, which is the type of apparatus of the present disclosure
  • FIG. 18 From the experimental data, a time series plot of model scale air chamber pressure (upper plot); and in the lower plot: adjacent incident wave probe water level (dashed line) and mean surface elevation (solid line);
  • FIG. 19 From the experimental data, the pneumatic power results for the test wave energy capture device derived from regular waves ( 237 data points);
  • FIG. 20 From the experimental data, the pneumatic efficiency for the test wave energy capture device derived from regular waves ( 237 data points).
  • This disclosure relates to the features of an apparatus for extracting energy from an oscillating working fluid, for example ocean waves repeatedly entering and leaving the apparatus in use.
  • the disclosure also relates to the features of the apparatus which maximise the capture of the incoming waves.
  • the disclosure also relates to a method of operating and controlling the apparatus to maximise the quantity of energy generated.
  • the apparatus has a design which enables greater energy generation per unit flow of fluid than known techniques in this field.
  • the apparatus shown in FIGS. 1 and 2 comprises a duct 10 , also referred to herein as “the apparatus” and “oscillating wave column device,” having two arm portions 12 , 14 , each arm comprising an elongate conduit which is generally rectangular in cross-section and arranged orthogonally to one another and connected in a generally L-shaped configuration, when the duct 10 is viewed from the side.
  • the apparatus also referred to herein as “the apparatus” and “oscillating wave column device”
  • each arm comprising an elongate conduit which is generally rectangular in cross-section and arranged orthogonally to one another and connected in a generally L-shaped configuration, when the duct 10 is viewed from the side.
  • the first conduit 12 of the duct 10 is arranged in use to be substantially submerged below the mean surface level (MSL) of a body of water 16 in which it is located, for example to rest on the sand and rock base 18 at an ocean shoreline, and oriented with its elongate axis oriented generally horizontally to be aligned with the sand and rock base 18 .
  • MSL mean surface level
  • the first conduit 12 has a rectangular-shaped opening mouth 20 which is arranged for receiving an incoming wave flowing in from the body of water, the mouth 20 being oriented outwardly into the body of water which is the source of the waves, for example an ocean or lake.
  • the cross-sectional area of the mouth 20 is greater in area than at any point in the rest of the first conduit 12 , because the first conduit 12 tapers down in cross-sectional area when moving in a direction from the opening mouth 20 inwardly into the interior of the duct 10 and towards the second conduit 14 .
  • the effect of a general tapering of this solid-walled first conduit 12 is to accelerate the flow of incoming waves from the body of water 16 into the duct 10 , for reasons which will become apparent when an oscillating flow is created in use.
  • a part of the upper wall 22 of the first conduit 12 is sloped downwardly and is angled towards the flat base floor 24 , which rests on the sand and rock base 18 , in use.
  • Vertical side walls 26 extend between the flat base floor 24 and the upper wall 22 of the first conduit.
  • the tapering entry region of the first conduit 12 extends for about one third of the length of the conduit 12 , but this can be a different proportion in other embodiments.
  • the first conduit may comprise a sloped upper wall over its entire length, along with a flat base floor 24 and with vertical side walls 26 extending therebetween.
  • the first conduit can have an upper wall and a base floor which are both sloped inwardly towards one another over some of the length of the conduit, when moving in a direction from the opening mouth inwardly into the duct.
  • the side walls of the first conduit can also be angled to taper inwardly, to form a conduit with a narrowing width so that it has a cross-sectional area which reduces when moving in a direction from the opening mouth inwardly into the duct.
  • the outermost and uppermost region 28 of the mouth 20 of the first conduit 12 is arranged in use to extend above the MSL of the body of water 16 in which it is located, to form a wave-piercing lip 30 of the mouth 20 .
  • This feature can help to capture and channel a greater flow of incoming waves from the body of water 16 into the duct 10 , particularly if the motion of the body of water is rough or choppy.
  • the second conduit 14 of the duct 10 is arranged in use to be substantially extending above the MSL of the body of water 16 in which it is located, oriented with its elongate axis being generally perpendicular to that of the first conduit 12 .
  • the second conduit 14 is elongate and extends from the first conduit 12 , and is arranged for receiving water from the incoming wave after it has flowed through the first conduit 12 .
  • the second conduit 14 extends to a height above a maximum level of water 32 received from the incoming wave after it flows through the first conduit 12 .
  • a volume of gas typically air which is located above that maximum level of water 32 , can be displaced out of, and then drawn back into, the uppermost region of the second conduit 14 as will shortly be described.
  • first 12 and second 14 conduits also have a flow direction control segment in the form of a planar sloped portion 34 arranged at the junction of the two conduits 12 , 14 , which facilitates the flow of incoming water to be able to turn from a horizontal axial flow to a vertical axial flow orientation within the duct 10 , and subsequently from a vertical axial flow to a horizontal axial flow orientation when the water oscillates in the reverse direction and flows outwardly from the duct 10 toward the body of water 16 . If the cross-sectional area of first conduit 12 becomes narrower as the fluid progresses into the duct 10 , the fluid velocity will increase, which in turn can drive the fluid column formed within the duct 10 to oscillate more quickly.
  • a displaceable volume of air which can exit the uppermost region 36 via a number of flow control devices in the form of butterfly or one-way check valves 38 , which can be opened automatically, or arranged to swing or to move open.
  • the uppermost region 36 inside the second conduit 14 (and above the maximum level of water 32 ) defines a flow passage 40 , which is also in fluid communication with a unidirectional turbine 44 .
  • the valves 38 and turbine 44 are in direct fluid communication with the flow passage 40 , meaning that air movement into and out of the flow passage 40 does not pass through a valve before it reaches a turbine, or vice versa.
  • valves and turbine are not arranged in series with one another, but rather are arranged in a parallel operational configuration with one another, being positioned at discrete, spaced-apart openings in the walls of the flow passage chamber 40 , inside the second conduit 14 .
  • Such an arrangement allows for selectively changing the configuration of the flow passage 40 , so that the working fluid (such as air) can act unidirectionally on a turbine, or instead be operated in a bypass configuration (that is, bypassing the turbine) to flow unidirectionally via the discharge valves.
  • the working fluid such as air
  • bypass configuration that is, bypassing the turbine
  • FIG. 3 A the moment of inception of a wave moving toward the duct 10 is shown, with the wave piercing lip 30 and the narrowing cross-sectional area of the first conduit 12 serving to guide the incoming wave into the duct 10 .
  • FIG. 3 B the wave moves through the duct 10 in the direction of the arrows 42 , and some of the air in the flow passage 40 in the uppermost region 36 is displaced by the vertically rising water in the duct 10 , and flows out of the butterfly or one-way check valves 38 and is discharged to the atmosphere.
  • the valves 38 are arranged to have a lightly feathered movement, so that the flow of air out of the flow passage 40 is sufficient to open them, and to offer a path of least resistance out of the duct 10 , rather than for any significant quantity of air to leave the flow passage via a unidirectional turbine 44 .
  • the wave then moves back out of the duct 10 via the mouth 20 and towards the body of water 16 in the direction of the arrows 46 , which is in a direction opposite to the direction 42 of the incoming wave as depicted in FIG. 3 B .
  • the flow in the outward direction 46 atmospheric air is drawn into the flow passage 40 in the uppermost region 36 by a suction created by the departing water. Because the butterfly or one-way check valves 38 are now fully closed, the air can only be drawn in through the unidirectional turbine 44 , and this flow of air this causes the turbine 44 to turn so as to generate electrical energy.
  • the valves when atmospheric air is drawn into the flow passage 40 in the uppermost region 36 by a suction created by the departing water, the valves can be of a type, or arranged at a position of partial closure, which restricts air flow therethrough, rather than being completely closed to such air flow.
  • the majority of the air being drawn into the flow passage 40 is via the unidirectional turbine 44 .
  • the flow of air both into and out of the flow passage 40 is therefore responsive to, and generated by, oscillations of an oscillating water column in the duct 10 , which is set up by the repeated wave flow frequency in the particular location.
  • the flow situations shown in FIGS. 3 B and 3 C may be reversed, so that when the wave moves into the duct 10 , the air in the flow passage 40 in the uppermost region 38 is displaced by the rising water in the duct 10 to flow out of the unidirectional turbine 44 so as to be discharged to the atmosphere.
  • the wave moves out of the duct 10 via the mouth 20 and towards the body of water 16 , atmospheric air is then drawn back into the flow passage 40 via the valves 38 , which are arranged to be more easily opened in one direction into the flow passage 40 than the air flow which can be achieved into the flow passage 40 through a unidirectional turbine 44 .
  • Each arm portion 12 , 14 comprises an elongate conduit which is generally rectangular in cross-section and these portions are arranged orthogonally to one another and connected in a generally L-shaped configuration.
  • the first conduit 12 of the duct 10 is arranged in use to be substantially submerged below the mean surface level (MSL) of a body of water, and oriented with its elongate axis oriented generally horizontally to be aligned with the sand and rock base 18 .
  • MSL mean surface level
  • In the uppermost region 36 of the second conduit 14 are a number of flow control devices in the form of butterfly or one-way check valves 38 , which can be opened automatically, or arranged to swing or to move open.
  • the uppermost region 36 inside the second conduit 14 (and above the maximum level of water 32 ) defines a flow passage 40 , which is also in fluid communication with a unidirectional turbine 44 .
  • Geometrical design features adopted by the inventor include the introduction of the sloped front lip and pointed bow 33 , shown in FIG. 5 , to reduce wave loads on the front face of the duct 10 .
  • FIGS. 14 and 15 a duct 10 of a somewhat different appearance is shown. In all respects it is functionally similar to the previously described embodiment. Like part numbers are used to illustrate functionality.
  • the valves 38 are fitted with a control mechanism to control their opened and closed configurations.
  • the valve may have a gate which can be opened and closed to the flow of gas by a hinged movement, or by a sliding movement or by a rotatable movement to at least cover a part of the cross-sectional opening passage of the valve.
  • the valves used can be configured in any other appropriate orientation to respond to changes in the pressure and/or direction of flow of the oscillating air entering and leaving the flow passage 40 .
  • the access to the displaceable gas in the flow passage 40 in the uppermost region 36 of the second conduit 14 can be via one or more valves 38 (or other forms of flow control devices) as well as via the unidirectional turbine 44 , it is possible for the system to be configured to operate each form of access to the flow chamber separately, and sequentially, to the other. By doing so, this means that the design of the turbine 44 can be considerably simpler than the arrangements in prior art oscillating water columns for power generation, many of which have focussed on the development of new turbine designs which can cope with a bi-directional air flow using a turbine which rotates unidirectionally on a shaft.
  • the gas in the flow passage in the uppermost region of the second conduit is displaced by the vertically rising water in the duct, and flows out of a unidirectional turbine and becomes discharged to the atmosphere, but when gas is drawn back into the flow passage by suction, it needs to flow via the same unidirectional turbine but in the opposite direction, which necessitates an adjustable flow turbine design of great complexity.
  • the turbine 44 is of a basic known design, and includes a rotor 48 comprising a central hub 50 located on one end of a rotatable shaft, and a plurality of blades 52 arranged about and extending from the periphery of the hub 50 , the rotor 48 being disposed within a housing 54 in fluid connection with the flow passage 40 .
  • the shape of the turbine blades 52 and their orientation in relation to the hub 50 facilitates unidirectional rotation of the turbine rotor 48 in response to a unidirectional axial flow of gas through the turbine housing 54 .
  • an electric generator is configured for rotation by the turbine to generate electrical energy, and is connected to the end of a drive shaft of the turbine 44 , at the other end of the drive shaft to the location of the hub 50 .
  • the system described has other significant operation advantages over the known prior art because of the ability to adjust the orientation of the valves 38 to respond to changes in the pressure and/or direction of flow of the oscillating air. For example, it is possible to “tune” the frequency of the oscillating water column in the duct 10 to match the frequency of movement of an incoming and outgoing wave from the ocean by opening or closing a number of the valves 38 located at the second conduit 14 in the portion which extends above the MSL. By doing this, the air pressure resistance in the flow passage 40 in the uppermost region 36 of the second conduit 14 which faces against the rising water in the duct 10 , can be adjusted.
  • the frequency of the oscillating water column which flows into and out of the duct 10 substantially corresponds to the frequency of the incoming and outgoing waves from the body of water 16 , then the operation of the energy extraction apparatus will be smoother and more efficient, rather than needing to operating in a situation where the oscillating flows in the duct 10 are constantly out of sequence with the waves, and therefore subjected to extra turbulence and inefficient draw of air into the turbine 44 .
  • Such a “tuning” of the frequency of the oscillating water flow in the duct can be performed continuously, depending on the prevailing ocean wave conditions, for example by automating the adjustment of the valve openings by using a control mechanism which is responsive to measured changes in the pressure of incoming and outgoing waves.
  • the control mechanism can selectively open or close (or partially open or close) one or more of the valves 38 .
  • This adjustment can change the available cross-sectional area of openings to and from the flow passage 40 in the uppermost region 36 of the second conduit 14 of the duct 10 , as a proportion of the total surface area of that second conduit 14 which lies above the MSL, such a proportion now defined by the inventor as an “optimum venting ratio”.
  • the optimum venting ratio is less than 15%, but an optimum venting ratio of less than 10% can also be suitable.
  • a lower or higher optimum venting ratio may be required, for example as low as 1%, in order to optimise the time that the oscillating water flow spends in the duct 10 .
  • valve opening control mechanism can be used to close and lock down a sufficient number of the valves 38 so that a head of air pressure is established within the flow passage 40 .
  • Such “de-tuning” can act as a safety feature by excluding the strongest waves from the ocean from reaching as far up into the duct, and in doing so, possibly protecting the valves and turbine from storm damage.
  • the uppermost region 36 of the second conduit 14 of the duct has four butterfly valves 38 shown on the rear, upper, vertical side wall 56 of the duct 10 , and three butterfly valves 38 shown on the top horizontal wall 58 of the uppermost region 36 of the second conduit 14 .
  • more or less than this number of valves 38 can be installed at the time of the initial construction of the duct, depending on the location and expected ocean wave severity that will be encountered, thereby being a design feature which changes the possible maximum venting ratio of the particular duct.
  • the type of valve can also be varied, and also combinations of different types of valves are possible to be fitted on one duct too (butterfly, one-way check valves, and so on).
  • valve(s) 38 Once the repeated steps of opening the valve(s) 38 as the wave enters the duct 10 , followed by valve(s) 38 closing and air being drawn into the second conduit 14 via the turbine 44 as the wave leaves the duct 10 , have reached a stable pattern, the turbine 44 and generator will generate electrical energy which can be conveyed from the duct 10 (if located offshore) to the land (on the shore) by means of an insulated high voltage copper cable.
  • a typical duct has a first conduit length of around 8-10 metres, and a second conduit which extends 15-18 metres above the base surface of the body or water or ocean shoreline at which it is located.
  • the structure of the duct is typically made of reinforced concrete, so as to have the weight and strength to be able to withstand the pressure of repeatedly being struck by ocean waves, in a corrosive salty environment.
  • the inventor has discovered from experimental results using the new energy extraction apparatus that there is a significant increase in the energy capture from a unidirectional turbine 44 which is configured to operate with a unidirectional flow of air, rather than a unidirectional turbine which is configured to operate with a bidirectional flow of air.
  • a unidirectional turbine 44 which is configured to operate with a unidirectional flow of air
  • the energy generated is 16% better than could be achieved using known bidirectional turbine designs with a flow operating in that same direction.
  • this improved result is caused by a combination of the downward hydrostatic pressure head of the oscillating water column located in the second conduit 14 , in addition to the suction draw of the body of water 16 , as it draws water out of the duct 10 . Therefore, because the present system can be configured to isolate the steps of both expulsion out, and suction in, of air in relation to the flow passage 40 using different devices, it is possible to capture energy solely from the gas flow which operates in response to the wave outflow from the duct, which is also the flow with the highest potential energy.
  • the inventor has also discovered from experimental results using the new energy extraction apparatus that there is a significant increase in the energy capture when the feature of the wave piercing lip 30 is added to the opening mouth 20 of the first conduit 12 .
  • the accelerated delivery of flow of the incoming waves into the duct 10 results in a further improvement of 20% in the energy able to be generated when compared with known oscillating duct apparatus without such a feature. It is believed that this feature brings more fluid into the duct 10 , which in turn subsequently causes more air to be drawn into the flow passage 40 in the second conduit 14 via the turbine 44 as the wave leaves the duct 10 .
  • the wave piercing lip 30 of the present disclosure is arranged so that it is almost always visible above the MSL of the waves at a particular location.
  • the dock 35 In a non-submerged state, the dock 35 is able to be moved by towing behind a shipping vessel 37 for in-water location of the apparatus 10 .
  • the oscillating wave column device 10 is itself fitted with flotation aids 41 for use when needed for positioning at the final stage.
  • the assembled oscillating fluid duct Once the assembled oscillating fluid duct is ready for installation, it is positioned on the said submersible floating dock (or is built atop a platform thereof during the construction phase).
  • the non-submerged floating dock and the duct can be towed behind a shipping vessel, for example a tugboat, using long cables 39 , to be moved in a direction toward the pre-determined destination of the apparatus on the body of water, such as an ocean edge/surf edge region.
  • the floating dock When near the final location, the floating dock can be submersed and the duct remains afloat in the water by its own flotation aids.
  • flotation aids can be in many forms, such as hollow buoy panels, inflatable gas balloons, and the like.
  • the submersible dock provides great advantages such as stability of handling such a sizeable apparatus when moving across open ocean to reach a remote coastline for final installation.
  • the floating dock minimises the risk of capsizing or sinking of the duct apparatus in rough weather.
  • Prototype top lip and front wall geometry are design features which appear to positively affect the operational characteristics of the device. Experimental results indicate this unidirectional prototype will exhibit very good energy harvesting capability over a wide range of wave frequencies.
  • the OWC is a large hollow concrete chamber, partially submerged and sitting on the seabed and vented to the ocean through an underwater opening.
  • the chamber also includes a small opening to the atmosphere above the water line, in which is housed an air turbine.
  • a conventional stator plus rotor type turbine design was developed by the inventor for extracting power from the air flow induced by the pneumatic pressure of the OWC.
  • the single stage turbine operates on unidirectional air inflow over a wide range of pressure drop conditions.
  • the predicted turbine efficiency against turbine differential air pressure (op) is presented in FIG. 16 which was generated with the Aoleus meanline turbine performance analysis.
  • the weighted average turbine efficiency over the range of typical operation, down to ⁇ 30 kPa (measured as the product of torque multiplied by angular velocity, divided by pressure drop multiplied by volume flow rate), is 77% based on a constant turbine rotational speed of 650 RPM.
  • Geometrical design features adopted by the inventor include the introduction of the sloped front lip and pointed bow, which is shown most clearly in FIG. 5 . These geometric enhancements were included with the view to improving the hydraulic performance and reducing wave loads on the OWC front face.
  • King Island is situated in the western waters of Bass Strait, approximately equidistant between Georgia and the Australian mainland.
  • the island with a population of approximately 1700, is powered by its own grid system, consisting of wind turbines, some solar, battery storage, and complemented by diesel power generation.
  • the pilot plant project on King Island is located at a mean sea level depth of 10 metres, approximately 700 m from shore.
  • the new design of OWC device for this project will be 20 metres wide, with a nominal peak electrical generating capacity of 1 MW.
  • the wave climate for this location is greater than 45 kW/m, which rates it as one of the best in the world in terms of wave energy resource. Bathymetric surveys and sub-bottom profiling of the proposed site, which is located close to a suitable grid connection, has been completed.
  • the 1:30 scale model was manufactured from plywood with clear acrylic sides to enable visual observation of the internal chamber water level. 3D printed passive check valve bodies are fitted in the back and side of the model, and an acetate sheet is lightly hinged to the top edge of the body permitting the valve to open with minimal positive chamber air pressure.
  • the Power Take-off (PTO) was simulated using an orifice plate which exhibits a non-linear pressure/flow relationship similar to that of the single stage turbine.
  • Air chamber differential pressure was monitored with three separate pressure transducers (1 psi Honeywell TSC sensor conditioned by an Ocean Controls instrument amplifier KTA 284), one on each side of the chamber roof and one in the side of the top clear box. Each pressure sensor was found to produce near identical values (see FIG. 18 for example). Chamber water surface elevation was monitored by six resistive wave probes. Wave probes were connected to the data acquisition system through a HR Wallingford wave probe signal conditioning box.
  • Data was acquired at a rate of 200 Hz using a 16 bit National Instruments PCI card (NI PCI-6254) connected to a BNC terminal box. Data recording was trigger by wave paddle motion and was recorded for a duration of 30 seconds for regular waves and 600 seconds (30 minutes full scale equivalent) for irregular waves.
  • NI PCI-6254 National Instruments PCI card
  • ⁇ p air chamber differential pressure and Q is the air volumetric flow rate.
  • C d 0.6 is the orifice discharge coefficient
  • a o (moth m 2 is the restriction orifice cross-sectional area
  • ⁇ energy density (energy per unit surface area)
  • C g wave group celerity solved for the intermediate water depth
  • h wave height measured crest to trough.
  • Average irregular wave power is
  • h m 0 4 ⁇ square root over (m 0 ) ⁇ , with ⁇ square root over (m 0 ) ⁇ being the first spectral moment (equal to one standard deviation of the wave record), and T e is the energy period (m ⁇ 1 /m 0 ) (derived from spectral analysis).
  • Pneumatic efficiency is defined as the ratio of the pneumatic power extracted divided by the equivalent wave power across the width of the device
  • W device width facing the wave front.
  • FIG. 17 shows an energy balance for an OWC with an additional path for air valves.
  • the solid lines and arrows show the possible direction of flow of the energy in the system.
  • the dashed lines show less significant energy flow connections. For 100% pneumatic conversion efficiency, all of the energy must flow from the incoming wave (source) through to the Power Take-off (sink).
  • pneumatic power is the product of air differential pressure ( ⁇ p) and air flow rate (Q). Energy lost through the air valves (and potentially PTO depending on turbine geometry) for this half of the cycle is the integral of the pneumatic power for that duration.
  • Equation (1) Since the main objective is to minimise conversion losses, power consumed by the valves must be minimised. After physical consideration of Equation (1) this is only achievable by minimising the pressure differential, since air flow should be unimpeded to enable maximum energy storage as water column heave. Practically this is achieved by maximising air valve area and utilising valves with low back pressure.
  • FIG. 18 is a plot of experimental data which shows the relationship between the air chamber pressure, the chamber water column heave (storage) and the passing water surface profile adjacent to the water column (incident waves). It is evident the air chamber pressure is only slightly positive while the chamber water level (minimal energy loss through air valves) is rising and is significantly negative while the chamber water level is falling.
  • Results are presented in the following section for device power performance in head seas when exposed to both regular and irregular waves. Both full scale extrapolated results and efficiency results are presented.
  • FIG. 19 shows regular wave pneumatic power results extrapolated to full scale. Results were compiled from 237 separate runs of the wave maker. Due to deviation in the generated wave heights from desired, a linear correction (1+(h D ⁇ h A )/h D where h D is desired height and h A is actual crest to trough height) to pneumatic power was applied. For the larger wave heights (2.7 and 3.0 m) the power output appears somewhat erratic, which was found to be affected by a pressure loss from the chamber as the water level in the chamber dropped sufficiently for a separate atmospheric connection between the chamber and atmosphere past the front lip.
  • FIG. 20 shows the pneumatic efficiency of the device operating in regular waves.
  • the peak efficiency was seen to occur at just below 8 seconds with a value of between approximately 1 and 1.1 (improving for lower wave heights).
  • the predicted full scale pneumatic power matrix results were calculated from a total of 47 different wave records using a griddata function to perform 2D linear interpolation. Similar to what was found in the regular wave results; pneumatic power production was best towards the lower period waves with peak mean power production occurring between 11 and 13 second peak period (T p ). Similarly, efficiency is well over 0.5 for all T p up to 13 second inclusive.
  • Air compressibility is known to yield lower pneumatic performance for real seas compared to Froude scale extrapolated model test results.
  • Others have investigated the issue using a 3D numerical code and found the overestimation is in the order of 12% for a conventional OWC PTO. This simple correction can be applied to performance estimates by reducing pneumatic power extrapolated results accordingly.
  • the reduction in efficiency is a function of the air compressible volume. Since the new concept OWC of this disclosure causes the chamber water elevation to rise higher, the chamber air volume is consequently reduced. However, since the concept involves only rarefaction and not compressibility, it is likely a 12% estimate of the scaling error is somewhat extreme.
  • the conservative flow coefficient of 0.6 is a sufficiently conservative estimate in this case to compensate for any scaling issues.
  • the wave to wire efficiency of the system is colloquially described as “power out divided by power in”.
  • the average ‘power out’ of the proposed King Island pilot plant device has already been estimated (see above) at 472 kW.
  • the ‘power in’ is defined as the average incident wave energy density (kW per metre of wave crest) multiplied by the width of the device (in metres).
  • a detailed assessment of the wave climate at the King Island site indicates an average incident wave energy density of 52.87 kW/m. Multiplying by the device width of 20 metres suggests an average wave power incident upon the WSE device (‘power in’) of 1057 kW. Therefore, the wave to wire efficiency of the WSE device is estimated as 44.6%.
  • the apparatus disclosed herein has many advantages over convention power generation devices, as well as previous OWC technologies:
  • the foregoing describes only some embodiments of the inventions, and alterations, modifications, additions and/or changes can be made thereto without departing from the scope and spirit of the disclosed embodiments, the embodiments being illustrative and not restrictive.
  • the particular L-shaped form of the duct 10 shown in the drawings may be different, with the two conduits 12 , 14 not necessarily orthogonal to one another.
  • the valves 38 may be different in size, shape and total number thereof.
  • There may be more than one turbine 44 on any particular duct 10 and these may be housed and connected to the uppermost region 36 of the second conduit 14 by other means (for example, via pipes).
  • the materials of construction of the duct 10 whilst typically made of concrete, can also be of other materials such as hard plastics or carbon fibre, and be anchored to the base 18 at the ocean shore. While reference has been made to wave generation from the sea or an ocean, wave generation can also occur from lakes, rivers and tidal pools, all of which are suitable for using the present method and apparatus.

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